Substrate via filling

ABSTRACT

A method for filling vias with metal includes receiving a substrate having vias, forming a metal plating layer over the vias on a first side of the substrate, fill-plating the vias with a first metal beginning with the metal plating layer on the first side of the substrate and advancing to a second side of the substrate to provide filled vias. The metal plating layer may be subsequently patterned to provide selected circuit connections or chemically-mechanically polished to completely remove the metal plating layer. Forming a metal plating layer over the vias may include filling the vias with a sacrificial filler to enable formation of the metal plating layer and subsequently removing the sacrificial filler via an etching operation or the like. In other embodiments, forming the metal plating layer over the vias is accomplished by bonding a metallic layer onto the first side of the substrate.

BACKGROUND OF THE INVENTION

The present invention relates generally to substrate manufacturing andmore particularly to filling vias in substrates such as glassinterposers.

Glass interposers are receiving more and more attention for variousapplications including 3D/2.5D integration and RF component integration.Ultra-thin glass substrates with through vias are now commerciallyavailable. However, high aspect-ratio via filling and handling remain achallenge.

SUMMARY

A method for filling vias with metal includes receiving a substratehaving vias, forming a metal plating layer over the vias on a first sideof the substrate, fill-plating the vias with a first metal—beginningwith the metal plating layer on the first side of the substrate andadvancing to a second side of the substrate—to provide filled vias. Themetal plating layer may be subsequently patterned to provide selectedcircuit connections or chemically-mechanically polished to completelyremove the metal plating layer.

Forming a metal plating layer over the vias may include filling the viaswith a sacrificial filler to enable formation of the metal platinglayer, and subsequently removing the sacrificial filler via an etchingoperation, or the like. In other embodiments, forming the metal platinglayer over the vias is accomplished by bonding a metallic layer onto thefirst side of the substrate. The vias may be etched to remove anybonding adhesive previous to the fill-plating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustration depicting one embodimentof an interposing packaging system that may be enabled by at least someof the embodiments disclosed herein;

FIG. 2 is a flowchart depicting a via-filling method in accordance withthe present invention;

FIGS. 3a-3g are cross-sectional illustrations of a substrate processedaccording to a first embodiment of the method of FIG. 2;

FIGS. 4a-4e are cross-sectional illustrations of a substrate processedaccording to a second embodiment of the method of FIG. 2; and

FIGS. 5a-5d are cross-sectional illustrations of a substrate undergoinga sidewall adhesion and via filling process in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

The embodiments disclosed herein enable via filling in thin substratesat high packing densities and aspect ratios such as is needed for glassinterposers. It should be noted that references throughout thisspecification to features, advantages, or similar language do not implythat all of the features and advantages that may be realized with thepresent invention should be, or are in, any single embodiment of theinvention. Rather, language referring to the features and advantages isunderstood to mean that a specific feature, advantage, or characteristicdescribed in connection with an embodiment is included in at least oneembodiment of the present invention. Thus, discussion of the features,advantages, and similar language, throughout this specification may, butdo not necessarily, refer to the same embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that theinvention may be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the invention.

These features and advantages will become more fully apparent from thefollowing description and appended claims, or may be learned by thepractice of the invention as set forth hereinafter.

The embodiments disclosed herein enable via filling in thin substratesat high packing densities and aspect ratios such as is needed for glassinterposers. For example, FIG. 1 is a cross-sectional view illustrationdepicting one embodiment of an interposing packaging system 100 that maybe enabled by at least some of the embodiments disclosed herein. Asdepicted, the interposing packaging system 100 includes an interposer110 with filled vias 120 that provide electrical connectivity to variousintegrated circuits 130 mounted above and below the interposer 110. Theinterposer 110 also provides electrical connectivity to a printedcircuit board 140 via various solder connections 150.

The integrated circuits 130 mounted on the interposer 110 may have aconnection (i.e., I/O) density that is greater than the connectiondensity achievable on the printed circuit board 140. Consequently, theinterposer 110 facilitates electrical connectivity between theintegrated circuits 130 and the printed circuit board 140 and may havevarious routed traces thereon (not shown) to facilitate the requiredelectrical connectivity in addition to the filled vias 120.

Despite the utility of the interposer 110, reliable and cost effectivefilling of the vias has been difficult. For example, filling high aspectratio vias within glass interposers often results in cracking, platingpinch-off, and incomplete filling. The present invention was developedin response to these issues.

FIG. 2 is a flowchart depicting a via-filling method 200 in accordancewith the present invention. As depicted, via-filling method 200 includesreceiving (210) a substrate comprising vias, forming (220) a metalplating layer over the vias, fill-plating (230) the vias, and removingor patterning (240) the metal plating layer. The via-filling method 200enables the filling of vias that have high aspect ratios (e.g. greaterthan 5:1) and packing densities (e.g. with a via pitch of less than 100um).

Receiving (210) may include receiving a substrate with vias formedtherein. For example, the vias may be formed with water jets, electricdischarge, or lasers. Forming (220) a metal plating layer over the viasmay include one of several approaches. In one embodiment, a metal foilis bonded onto one side of the substrate. In another embodiment, asacrificial material is inserted into the vias and the metal layer isdeposited on one side of the substrate. Subsequently, the sacrificialmaterial may be removed via etching or the like.

Fill-plating (230) the vias may be conducted according to methods knownto those skilled in the art—beginning with the metal plating layer on afirst side of the substrate and advancing through the via toward asecond side of the substrate. For example, the vias may be fill-platedwith a metal by an electroplating process known to those of skill in theart. Removing or patterning (240) the metal plating layer may includecompletely removing the metal plating layer or patterning the metalplating layer by selectively removing a portion of the metal platinglayer. Patterning the metal plating layer may result in signal tracesbetween selected filled vias.

FIGS. 3a-3g are cross-sectional illustrations of a substrate processedaccording to a first embodiment of the method of FIG. 2. As shown inFIG. 3a substrate 310 comprising vias 312 may be received and filledwith a sacrificial material 314 as shown in FIG. 3 b. Examples of asacrificial material include photoresist, PMMA, and various low solventpolymers. As shown in FIG. 3 c, a metal plating layer 316 may be formedover the vias 312. Subsequently, the sacrificial material 314 may beremoved as shown in FIG. 3d to provide a fillable substrate 320.

As shown in FIG. 3 e, the vias 312 of the fillable substrate 320 may befill-plated with a fill metal 332 beginning with the metal plating layer316 on one side of the substrate and advancing through the via towardthe other side of the substrate resulting in a filled substrate 330.Subsequently, the metal plating layer 316 may be completely removedresulting in the finished substrate 340 shown in FIG. 3 f.Alternatively, the metal plating layer 316 may be patterned resulting inthe patterned substrate 350 shown in FIG. 3 g.

FIGS. 4a-4e are cross-sectional illustrations of a substrate processedaccording to a second embodiment of the method of FIG. 2. As shown inFIG. 4 a, substrate 310 comprising vias 312 may be received and bondedto a metallic foil 410 as shown in FIG. 4 b. In the depicted embodiment,the metallic foil includes an adhesive layer 412, the metal platinglayer 316, and a backing layer 414. The backing layer 414 may be rigidor flexible. The adhesive at the bottom of the vias may be removed by anetching process, or the like, through vias 312, to expose the metalplating layer 316 and provide the fillable substrate 320 shown in FIG. 4c. The fillable substrate 320 may undergo fill-plating to provide filledsubstrate 330 shown in FIG. 4 d. Subsequently, as shown in FIG. 4e themetal plating layer 316 may be removed to provide the finished substrate340. Alternately, the metal plating layer 316 may be patterned toprovide the patterned substrate 340 (not shown in FIGS. 4a-4e ).

FIGS. 5a-5d are cross-sectional illustrations of a fillable substrate320 undergoing a sidewall adhesion and via filling process in accordancewith an embodiment of the present invention. As depicted in FIG. 5 a, afillable substrate 320 may be received and provided with an adhesionlayer 510 as shown in FIG. 5 b. For example, the adhesion layer 510 maybe a metal that is deposited via chemical vapor deposition, physicalvapor deposition, or electro-less plating. The adhesion layer 510 mayhave a CTE that is greater than the CTE of the fill-plated material andless than the CTE for the substrate.

Subsequent to deposition of the adhesion layer 510, the fillablesubstrate 320 may be fill-plated with a fill metal 332. Fill-plating mayadvance primarily from the metal plating layer 316 on one side of thesubstrate but may also advance from the adhesive layer 510. In certainembodiments, the CTE of the fill metal 332 is controlled byco-depositing a metal with a relatively high CTE along with a low CTEmaterial such as carbon nanotubes. In one embodiment, the CTE is variedwith deposition depth to create a CTE gradient for the fill metal 332.For example, the CTE may be varied by reducing the deposition rate ofthe low CTE material as relative to the high CTE material as the viasare filled. The use of a CTE gradient may provide greater structureintegrity for the filled vias over wide temperature ranges and swings.Subsequently, as shown in FIG. 5 d, the filled substrate 330 may bepatterned or chemically mechanically polished on one or both sides toprovide a finished substrate 340 or a patterned substrate 350 (not shownin FIGS. 5a-5c ).

It should be noted that this description is not intended to limit theinvention. On the contrary, the embodiments presented are intended tocover some of the alternatives, modifications, and equivalents, whichare included in the spirit and scope of the invention as defined by theappended claims. Further, in the detailed description of the disclosedembodiments, numerous specific details are set forth in order to providea comprehensive understanding of the claimed invention. However, oneskilled in the art would understand that various embodiments may bepracticed without such specific details.

Although the features and elements of the embodiments disclosed hereinare described in particular combinations, each feature or element can beused alone without the other features and elements of the embodiments orin various combinations with or without other features and elementsdisclosed herein.

This written description uses examples of the subject matter disclosedto enable any person skilled in the art to practice the same, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the subject matter is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims.

What is claimed is:
 1. A method for filling vias on a substrate withmetal, the method comprising: receiving a substrate comprising aplurality of vias; forming a metal plating layer over the vias on afirst side of the substrate to provide a fillable substrate;fill-plating the vias with a fill metal to provide a filled substrate;and removing at least a portion of the metal plating layer from thefilled substrate to provide a finished substrate.
 2. The method of claim1, further comprising filling the vias with a sacrificial fillerprevious to forming the metal plating layer over the vias.
 3. The methodof claim 2, further comprising removing the sacrificial filler withinthe vias subsequent to forming the metal plating layer.
 4. The method ofclaim 1, wherein fill-plating comprises electroplating that generallyprogresses from the metal plating layer to a second side of thesubstrate.
 5. The method of claim 2, wherein filling the vias with asacrificial filler comprises filling the vias with a solvent-basedpolymer and evaporating a solvent from the solvent-based polymer.
 6. Themethod of claim 2, wherein forming the metal plating layer over the viascomprises depositing a metal.
 7. The method of claim 1, wherein formingthe metal plating layer over the vias comprises bonding a metallic layeronto the first side of the substrate.
 8. The method of claim 1, furthercomprising depositing an adhesion layer onto the walls of the viasprevious to fill-plating the vias.
 9. The method of claim 8, wherein theadhesion layer comprises a metal.
 10. The method of claim 1, wherein thefill metal has a coefficient of thermal expansion (CTE) that decreasestoward the center of the vias.
 11. The method of claim 8, whereindepositing occurs via electro-less plating.
 12. The method of claim 1,wherein removing at least a portion of the metal plating layer comprisespatterning the metal plating layer.
 13. The method of claim 1, whereinremoving at least a portion of the metal plating layer compriseschemical-mechanical polishing.
 14. The method of claim 1, wherein apitch for the vias is less than 100 um.
 15. The method of claim 1,wherein the substrate is an interposer.
 16. A method for filling vias ona substrate with metal, the method comprising: receiving a substratecomprising a plurality of vias; filling the vias with a sacrificialfiller; forming a metal plating layer over the vias on a first side ofthe substrate to provide a fillable substrate; removing the sacrificialfiller within the vias; fill-plating the vias with a first metal toprovide a filled substrate; and removing at least a portion of the metalplating layer from the filled substrate to provide a finished substrate.17. The method of claim 16, wherein fill-plating compriseselectroplating that generally progresses from the metal plating layer toa second side of the substrate.
 18. The method of claim 16, whereinfilling the vias with a sacrificial filler comprises filling the viaswith a solvent-based polymer and evaporating a solvent from thesolvent-based polymer.